Although Novacem's research efforts have yet to produce cement that's actually used in any construction projects, John Prendergast has ambitious plans for the product's future. "The aim is to develop a cement that can completely replace Portland cement," he says. In other words, he hopes any project that currently uses standard cement could seamlessly sub in Novacem's offering. Replacing one of the greatest sources of carbon dioxide emissions with a product that actually removes carbon dioxide from the environment would obviously be a very beneficial step forward.

There are a host of hurdles, however, that any of the producers of carbon neutral or negative cement will have to overcome. Perhaps most important is simply the manufacture of a reliable product that can, in fact, take the place of Portland cement -- this, of course, will only truly be tested once the companies unveil their cement for commercial applications. Although, according to Prendergast, Novacem has internal results that indicate it will be able to produce a cement that is every bit as strong as Portland cement.

But other questions loom as well. For carbon negative cement to actually replace its much dirtier counterpart, all of the raw materials for its production must be cheap and abundant enough to compete with Portland cement on a cost basis. Calera, for instance, has been criticized because its process necessitates access to rare and expensive alkali deposits -- an accusation the company disputes [source: Romm].

For its part, Novacem attests that access to the raw materials it requires is not a potential barrier at all. Nor, says Prendergast, is cost. In other words, soon after getting up and running, he expects that Novacem cement will have about the same price tag as Portland cement. "Initially, you need to build a few plants before you get cost parity," he says. "Our processing is different, but the engineers we have looking at the process so far estimate that the costs would be about the same."

Acceptance by the building industry and regulators could come as the product proves itself in the marketplace. Then again, if carbon negative cement can be produced at the same price and with the same quality of Portland cement, it's hard to imagine that it won't eventually be embraced.